- Jul 27, 2015
Researchers at the security consultancy Dolos Group, hired to test the security of one client’s network, received a new Lenovo computer preconfigured to use the standard security stack for the organization. They received no test credentials, configuration details, or other information about the machine. An analysis of the BIOS settings, boot operation, and hardware quickly revealed that the security measures in place were going to preclude the usual hacks, including:
With little else to go on, the researchers focused on the trusted platform module, or TPM, a heavily fortified chip installed on the motherboard that communicates directly with other hardware installed on the machine. The researchers noticed that, as is the default for disk encryption using Microsoft’s BitLocker, the laptop booted directly to the Windows screen, with no prompt for entering a PIN or password. That meant that the TPM was where the sole cryptographic secret for unlocking the drive was stored.
- pcileech/DMA attacks because Intel’s VT-d BIOS protection was enabled
- Authentication bypasses using tools such as Kon-boot
- Use of tools such as LAN turtle, Responder to exfiltrate data from USB ethernet adapters
Microsoft recommends overriding the default and using a PIN or password only for threat models that anticipate an attacker with enough skill and time alone with an unattended target machine to open the case and solder motherboard devices. After completing their analysis, the researchers said that the Microsoft advice is inadequate because it opens devices to attacks that can be performed by abusive spouses, malicious insiders, or other people who have fleeting private access. “A pre-equipped attacker can perform this entire attack chain in less than 30 minutes with no soldering, simple and relatively cheap hardware, and publicly available tools,” the Dolos Group researchers wrote in a post, “a process that places it squarely into Evil-Maid territory.”
The writeup shows how security is an iterative process that involves defenders putting new measures in place, attackers learning how to knock them down, and defenders revising those defenses or adding new ones. Defenses like full-disk encryption with BitLocker, locked BIOSes, UEFI SecureBoot, and TPMs can only go so far before someone finds ways to defeat them, at least given certain types of common configurations. Now, it’s on defenders to figure out where to go from here.